&#34;exclusive or&#34; logical circuit



Dec. 8, 1964 c. J. CREVELING 3,160,819 "EXCLUSIVE 0R" LOGICAL cmcuzw Original Filed Oct. 29, 1956 PULSE GENERATOR PULSE GENERATOR Pu LsE GENERATOR PU LSE GENERATOR INVENTOR CYRUS J. CREVELING BYMQZM, W fly-m/ ATTORNEY United States Patent 3,160,819 EXCLUSWE 0R LGGICAL ClRCiHT Cyrus J. Creveling, Oxon Hill, Md, assignor to the United States of America as represented by the Secretary of the Navy Original application Oct. 29, 1956, Ser. No. 619,099, now Patent No. 3,106,683, dated Oct. 8, 1963. Divided and this application Apr. 25, 1962, Ser. No. 190,184

1 Claim. (Cl. 328-93) (Granted under Title 35, 11.5. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This application is a division of application Serial No. 619,090, now Patent No. 3,106,683 filed October 29, 1956.

This invention relates to pulse transfer logical circuits and more specifically to such circuits known as exclusive or circuits. An exclusive or circuit is one having a plurality of input terminals and a single output terminal at which a pulse is produced when a pulse is applied to one and only one of the input terminals. Considering a circuit with two input terminals, then no output pulse is produced when both input terminals receive pulses or when neither receive input pulses.

Logical circuits are used throughout complex computer circuitry for a variety of purposes including performing logical operations or binary numbers, and many such computers must contain a great number of logical circuits to properly perform complex calculations. It therefore becomes essential that the individual circuits be made as simple and with as few elements subject to failure as possible, if the complete computer is to be reliable and have a minimum of down time. A great many logical circuits are known in which vacuum tubes are used to perform computing functions, however, these circuits are not as reliable as circuits using magnetic or semiconductor elements to perform these operations. Magnetic core logical circuits are known which can be used in an ex clusive or operation, however, such circuits are relatively complex in comparison with the present invention.

Accordingly, an exclusive or circuit is provided which has as its basic component a simple transformer with input terminals provided at both ends of the primary winding for applying a pulse or signal between these terminals and ground. The secondary winding of the transformer has a center-tap which is grounded and two diodes connected to produce an output pulse of desired polarity regardless of the polarity of the signal induced in the secondary. If either input terminal receives a pulse, an output will result of the desired polarity, but if pulses coincident in time and of equal amplitude and width are received at both inputs to the primary no current will flow in the primary, no voltage will be induced in the secondary and hence no output pulse will result. Thus a very simple logical circuit has been provided which is dependable in operation and which will contribute greatly to computer reliability.

It is an object of the present invention to provide an electrical logical circuit which produces an output when either one or the other of its input terminals receives a pulse, but produces no output when pulses coincident in time and of equal amplitude and width are received at both input terminals.

It is a further object of the present invention to provide v an electrical logical circuit of the exclusive or type which 3,160,819 Patented Dec. 8, 1964 becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a schematic representation of the exclusive or circuit of the present invention;

FIG. 2 is a schematic representation of another embodiment of the invention in which the resistors shunting the signal sources are eliminated; and 7 FIG. 3 illustrates still another embodiment in which diode limiters are employed to insure input signals of equal amplitudes.

Referring to FIG. 1, there is shown a transformer 10 which has a primary Winding 11 and a secondary winding 12. Resistors 14 and 15 are connected across the terminals of the primary winding and their common connection is grounded at 16. Input terminals 17 and 18 are provided for applying two input signals to the device, one between the ground connection 16 and terminal 17 and the other between ground 16 and terminal 18.

The output side of the device comprises a secondary winding 12 having a grounded center-tap 21, diodes 22 and 23 which are preferably germanium diodes but which may obviously take the form of selenium rectifiers or vacuum tubes, or the like and an output terminal 24.

Two signal generators 19 and 20 are connected between ground and the terminals 17 and 18. When only one signal is applied current flows through the primary winding 11, through the resistor positioned opposite the source which produced the signal and through the other signal generator, if said generator has a low impedance to ground. For example, if signal generator 19 produces an output pulse, current will flow through the primary 11, through resistor 15 and signal generator 20 to ground. As a result of current flowing in the primary winding a voltage is induced in the secondary winding 12 and an output pulse will appear at the output terminal 24.

If a positive input pulse is applied to the terminal 17 a positive output will appear at terminal 24, as the upper side of the secondary 12 will go negative with respect to ground and the lower side will go positive with respect to ground, thus current will flow through diode 23 and a positive pulse will be developed at the output. Similarly, if a positive pulse is applied to the terminal 18, the upper end of the winding 12 will go positive with respect to ground and current will flow through diode 22 and a positive pulse will be developed at the output. Thus, voltage induced in the secondary of either polarity as a result of the positive pulses or negative pulses introduced into the two inputs will result in a positive output pulse. Signals or pulses which are equal in amplitude and duration applied across either terminal 17 or 18 will result in identical output pulses.

It is contemplated that the input pulses applied to terminals 17 and 18 will be quantized, that is, will be coincident in time and of equal amplitude and duration and as pointed out above if one input 17 or the other input 18, but not both, receive such a pulse an output at terminal 24 will result, but if these quantized pulses are applied to both input terminals 17 and 18, the upper and lower ends of the primary winding 11 will be at the same potential, no current will flow in the primary 11, no voltage will be induced in the secondary winding 12 and hence no output will result at terminal 24. It should be pointed out that if two pulses of unequal amplitude are applied simultaneously to input terminals 17 and 18, an output will appear at terminal 24 which is proportional to the difference in the two amplitudes. In this regard, the values of the resistors 14 and '15 can be set so that pulses of equal amplitude are developed across the primary winding 11, ir-

respective of their originysignal generator 19 or signal generator 20. Although it is contemplated that signal generators 19 and 20 will produce quantized pulses, a

condition should signal generators 19 or 20 to produce pulses of unequal amplitude. A change in the value of resistors 14 or will only be effective to provide input pulses of equal amplitude if the differences between the amplitudes of the pulses produced by signal generators 19 and are constant. If the differences are not constant a circuit as shown in FIG. 3 is necessary. 7

As shown in FIG. 2, the resistors 14 and 15 areunnecessary if the signal sources 19 and 20 have impedance values to ground sutficie'ntly low to permit an appreciable current flow in the primary winding 11 and if the two signal generators 19 and 20 produce output pulses of equal amplitude; With the resistors 14 and 15 removed, a pulse applied to terminal 17 by the signal generator 19 will produce a current in the primary winding 11 and return to ground through the opposite pulse generator 20. Conversely, if an input pulse is applied to terminal 18 by means of pulse generator 20, current will flowthrough the primary winding 11 and return to ground through the opposite pulse generator 19. Thus, if the impedance of pulse generators 19 and 20 is low, an appreciable current in the primary Winding 11 will result and a voltage sufficient to produce a usable output at terminal 24 will be induced in the secondary winding 12. If the impedance of the pulse generators 19 and 20 is high, very little current would flow in the primary winding 11 and resistors 14 and 15 are necessary to provide a sufficiently low impedance path to ground to secure a usable current in primary 11. In other respects the logical circuitof FIG. 2- functions the same as that shown in FIG. 1.

Referring to FIG. 3, ther'e is shown a logical circuit similar to that of FIG. 1 but with the addition of series resistances 25 and 26 and diodes 27 and 28 which may be any unidirectional current device, for example, a silicon or germanium diode, connected across .the terminals of the primary winding 11. As pointed out previously, if the pulses supplied to the input terminals 17 and 18 by the signal generators 19 and 20 are of diifer ent amplitude but that difference is not constant, changing of the value of the resistors 14 or 15 will be ineffective to provide pulses of equal amplitude across the primary winding 11. In this. situation, where the diiferences in pulse amplitudes are not constant, the diodes 27 and 28 ,will effectively limit the amplitudes of thepulses applied to terminals '17 and 18 so that the pulses will be of equal amplitude.

A' terminal of diode 27 is connected to a terminal of diode 28 by a lead 31 and these two terminals are'biased to a certain positive potential by the battery 32. a The value of the bias potential is normally determined by the minimum positive pulse potential which either of the signal generators 19 or 20 is expected to produce. The diodes 27 and 28 are so connected that neither conducts when positive pulses which do not exceed the bias potential are applied to either terminal 17 or 18 or to both said rterminals,the diodes-then appearing as open switches and pulse potential applied to either or both of the terminals.

17 or 18 by the pulse generators 19 and 20 will normally exceed the bias potential because the bias potential is set change in valueof either resistor 14 or 15 will insure that 1 at the value of the minimum positive pulsepotential which 2 either signal generator is expected to produce. Therefore either or both of the diodes 27 and 28 conduct acting essentially as closed switches to connect the ends of the transformer primary 11 tothebattery 32. Thus at no time can the positive pulse potential at the ends of the transformer winding exceed the value of the bias potential. This difference between the input pulse potential and the value of the bias potential appears as a voltage drop across the series resistors 27. and 28 as is the usual case in limiting circuits. Thus the value of the pulses produced by the signal generators 19 or 20 will be effectively limited so that the values of the pulses applied to the ends of the primary'winding 11 will have the same amplitude. 'It is obvious that a similar circuit could be used if the pulse generators 19 and 20 produce negative pulses by reversing the connection of the diodes 27 and 28 and biasing their common connection to a negative potential, the value of which is determined by the minimum negative potential which the pulse generators 19 and 20 are expected to produce.

It should be understood, of course that the foregoing disclosure relates to only preferred embodiments of the .invention and that, itisintended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention. I

What is claimed is:

An Exclusive OR logic circuit comprising a first input terminal for receiving a first input pulse,

a second input terminal for receiving a second input pulse,

a transformer having a primary and a secondary winda first resistor connected between one end of said transformer primary Winding andfsaid first input terminal,

a second resistor connected between the other end of said transformer primary and. said secondinputterminal, r

a pair of diodes each having an anode and a cathode,

I said cathodes? being connected together,

a positive voltage bias connected to the juncture of said cathodes,

the anode of one of said diodes being connected between said first resistor and said one end of said transformer primary winding,

the anode of the other of said diodes being connected between said second resistor and the other end of said transformer primary winding,

saidconnections to the ends of said primary winding constituting the only electrical connections to said primary winding,

a third resistor connected between the anode of one of said diodes and a point of reference potential,

a fourth resistor connected between the anode of the other of said diodes and said point of reference potential,

means connected to said secondary windingfor developing an output pulse of predetermined polarity irrespective of the polarity of the voltage induced in said secondary winding by said first or second input pulses,

whereby said output pulse is produced only when an input pulse-isapplied to a single one of either of said input terminals.

References Cited by the Examiner UNITED STATES PATENTS 2,731,571 1/56 Chance 307-88.5 2,785,305 3/57 Crooks et al 328-93 OTHER REFERENCES Dept. of the Army Tech. Manual ,TMll-672, Pulse Technique, October 1961, pages 15-18.

ARTHUR GAUSS, Primary Examiner. JOHN W. HUCKERT, Examiner. 

